Due to such advantages as low power consumption and narrow bezel, a market share of oxide TFT display substrates becomes higher and higher. However, an oxide TFT is very sensitive to moisture and H+ in the air, and oxygen in an oxide semiconductor may react with the moisture and the free-state H+. At this time, the oxide semiconductor may become a conducting region, and the TFT may fail as a switch, so a display defect may be adversely affected.
Usually, in the related art an insulation layer of the oxide TFT is made of SiNx or SiON. The SiNx layer is dense and has an excellent insulation property, so it has an excellent ability of blocking moisture and free-state ions such as Na+ and K+. However, the SiNx layer contains a large number of free-state H+, which may be easily diffused into a semiconducting region of the TFT, so the TFT may fail as a switch, and the yield of the oxide TFT display substrate may be significantly adversely affected. Although without any free-state H+, the SiON layer is loose and its ability of blocking the moisture and the free-state ions such as Na+ and K+ is very weak, i.e., the moisture and the free-state ions such as Na+ and K+ may easily enter layers of the oxide TFT display substrate. At this time, the properties of a pixel electrode and the TFT as well as the display effect may be adversely affected. In a word, the yield of the conventional oxide TFT display substrate is relatively low.